1,721,032 research outputs found
Effect of the microstructure in the optimization of geopolymeric membrane supports for microfiltration of wastewaters
No full textAlkali activated materials and geopolymers have attracted a lot of research interests in the last 20 years
thanks to their excellent performances in terms of mechanical, thermal and durability properties. In
addition, these materials show promising properties in terms of sustainability when compared to
traditional binders commonly used in the building sector (i.e., ordinary Portland cement) and to
traditional and advanced ceramics (i.e., membranes, adsorbents, and catalysts). Sustainability in
geopolymers can be reached by using a broad variety of industrial by-products as raw materials and
by ambient or low temperatures (< 100 °C) consolidation.
The aim of the present study was the optimization of microstructural properties of one-part
geopolymers, based on flash-sintered metakaolin and anhydrous sodium silicate, for microfiltration
membrane support in wastewater treatments. Investigated geopolymers were shaped by uniaxial
pressing and cured at 70 °C for 24 h. Several parameters in terms of mix design optimization (i.e., alkali
concentration and water content) and pressing pressure were investigated to obtain a microstructure
suitable for the preparation of the support of flat asymmetric membranes. Assessment of the total
open porosity and the pore size distribution was carried out by mercury intrusion porosimetry, while
microstructural observations were performed by field emission gun-scanning electron microscopy
(FEG-SEM) coupled with energy dispersive spectroscopy (EDS). It was found that pressing is a
particularly suitable shaping method for one-part geopolymers thanks to the use of low water amount
for the activation of the mix. In addition, increasing the water content (up to 15 wt%) and pressing
pressure (up to 20 MPa) allowed the formation of a dense geopolymeric gel, while alkalis
concentration, ranging between Na/Al = 0.7 and 1.1, did not strongly influence the microstructure.
Finally, the optimized parameters for producing flat support for microfiltration membranes are a Na/Al
molar ratio equal to 1.0, 12 wt% water content and 2 MPa of pressing pressure. These conditions
allowed to obtain the same range of open porosity and pore size distribution characteristic of ceramic
membrane support used for the same purpose
Interaction between sodium chloride and ammonium phosphate on Carrara marble: two laboratory approaches
No full textThe present paper aims at investigating the interaction between NaCl and diammonium hydrogen phosphate (DAP) solutions, in view of field consolidation of NaCl- contaminated substrates by DAP. Two different approaches were tested on marble: part of the specimens was treated by a single solution containing both NaCl and DAP (“NaCl+DAP” samples) and part of the specimens was subjected to a two- step treatment, consisting on preliminary contamination by NaCl and subsequent consolidation by DAP (“NaCl then DAP” samples). For each approach, different NaCl and DAP concentrations were tested. The new phases, formed after treatment, were characterized by FT-IR and SEM and their consolidating effect was assessed by ultrasonic measurements, in terms of increase in dynamic elastic modulus (Ed). To investigate the influence of the NaCl contamination on the durability of the consolidating treatments, consolidated specimens were repeatedly immersed in water, the solubilized ions were analyzed by ion chromatography and the possible decrease in consolidating efficacy was assessed by Ed. The results of the study point out that, following either approach, new calcium phosphate (CaP) phases were formed, identified by FT-IR as hydroxyapatite and/or octa-calcium phosphate. These new phases led to significant increases in Ed, which experienced some re- duction when the consolidated specimens were immersed in water. Nonetheless, the residual Ed was sensibly higher than in the untreated condition, indicating that a significant mechanical benefit was maintained. The “NaCl then DAP” samples, which resemble the actual situation in the field, seem to provide more reliable results than those obtained following the alternative approach. In fact, the combined treatment (“NaCl+DAP”) led to lower increases in Ed and less pronounced formation of new CaP, possibly because the presence of sodium and chloride ions in the DAP solution significantly altered the mechanisms of CaP formation
A preliminary study on the characterization of Recycled Asphalt pavement (RAP)
No full textThe replacement of natural aggregates with recycled ones for concrete production is of vital importance in view of increasing the sustainability of construction materials in accordance with the Circular Economy. The use of crushed Recycled Asphalt Pavement (RAP) as aggregates for concrete will allow the production of more sustainable materials in the construction field. However, chemical, physical and mechanical characteristics of RAP aggregates shall be investigated to optimise their use for concrete production. This issue is one of the tasks of the research project “Sustainable concrete made with recycled asphalt pavement (RAP-CON)” granted by Fondazione Cariplo, currently ongoing.
This study reports the first results on the characterization of five types of RAP collected from different Italian Highways. Several properties of RAP as aggregates for concrete were investigated in terms of microstructure, dimensional stability and durability. In particular, morphological observation was carried out by optical and scanning electron microscopy, while open porosity and pore size distribution was evaluated by mercury intrusion porosimetry. Dimensional stability was assessed by preparing cementitious mortar and concrete samples, following the accelerating curing described in EN 1367-4. Lastly, durability was investigated in terms of resistance to freeze and thaw cycles performed in accordance with EN 1367 (parts 1 and 6) in presence of distilled water and salts (1 wt% NaCl solution), respectively. It was found that RAP is a suitable material for aggregates in concrete. Depending on the adhesion between the bituminous binder and the natural aggregates, different durability performances can be achieved. Finally, different results have been obtained as function of types of RAPs, indicating that their characterization before concrete preparation is an important step to ensure the performance of the final product
Novel geopolymeric support for microfiltration membranes applied in wastewater treatment
No full textMicrofiltration membranes are widely used in wastewater treatment and are typically made of ceramic
or polymer materials. Despite the great durability of ceramic membranes, polymeric membranes are
very often preferred due to production costs. By using geopolymers, however, it is possible to obtain
microfiltration membranes with durability characteristics similar to those of ceramic materials, but
with considerably reduced production costs since geopolymers do not require a sintering treatment.
In this study, a geopolymer support for asymmetric microfiltration membranes is characterized in
terms of porosity and hydraulic permeability. The support was obtained by uniaxially pressing a dry
mixed powder consisting of metakaolin and anhydrous sodium silicate, sprayed with 12 wt% of water.
Curing was carried out at 70 °C for 24 hours and 6 more days at room temperature. The porosity of
samples pressed using 2 MPa (total open porosity of 39 % and a modal pore size of 23 μm) are
comparable to those of ceramic membranes for microfiltration [1]. The support permeability was
measured in a dead-end apparatus at a trans-membrane pressure varying from 0.2 to 0.5 bar, with
pure water and ethanol-water solutions. Hydraulic permeability of 30500 ± 3090 L/(h·m2·bar) was
obtained with 4 samples, whereas the use of 100 and 200 g/L ethanol-water solutions showed a
reduction in permeability to 26140 ± 2640 and 20820 ± 1430 L/(h·m2·bar) respectively. Further tests
performed on less porous samples obtained by pressing the powder at 5 MPa (total open porosity and
modal pore size of 27% and 15 μm, respectively) led to similar results. These initial characterizations
highlight the potential of this new material in the treatment of wastewater by membrane separation.
Future studies are ongoing to develop geopolymer selectives layer by dip coating to be applied on
geopolymer supports
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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